As the number of circuits per unit area has increased, particulates have become more of an issue for semiconductor wafers. The size of particulates that can destroy a circuit has decreased and is approaching the molecular level. Particulate control is necessary during all phases of manufacturing, processing, transporting, and storage of semiconductor wafers. Particle generation during insertion and removal of wafers into carriers and from movement of wafers in carriers during transport needs to be minimized or avoided.
Driven by economies of scale, the size of wafers utilized in semiconductor fabrication facilities (fabs) has continually increased. Currently there are a number of fabs that process 300 mm wafers. It is anticipated that soon the maximum size of commercially processed wafers will increase to 450 mm. With the significant leaps in the size of processed wafers, new issues and problems arise that were not present with smaller sized wafers.
For example, although wafer containers are often robotically handled such as by gripping robotic flanges on the top of the containers, they are still manually handled in many instances and typically come equipped with or have optional side handles. It is still relatively easy for personnel, by using such handles, to manually transport standardized 300 mm containers loaded with wafers as such containers often around weigh 20 pounds.
Standards for 450 mm wafers, such as the number of wafers in containers and the spacing between wafers, may very well remain the same as current 300 mm wafer container standards due to existing equipment compatibilities and cost pressures. And, of course, as wafers get larger in diameter, they correspondingly get heavier. A wafer container that holds the same number of 450 mm wafers as is provided in standardized 300 mm containers is expected to weigh approximately 40 pounds. At this weight, manual handling starts to become more difficult.
Using comparable thicknesses of polymer walls for a larger container may not provide sufficient structural rigidity of the container. That is, the container would be expected to be less dimensionally stable under loading, transfer and shipping due to the greater dimensions and greater expanses of polymer. Thickening the walls and adding significant strengthening structure would further increase the weight of 450 mm wafer containers.
Moreover, conventional 300 mm wafer containers are typically injection molded. It is anticipated that it will be difficult to adequately control the dimensions of larger containers utilizing comparable injection molding practices and comparable or larger wall thicknesses. Currently 300 mm wafer containers generally utilize the shell as the principal structural member for positioning components that interface with wafers and outside equipment, namely the wafer supports and the kinematic coupling machine interface.
In addition, the open interior volume will significantly increase as will the area of the open front that sealingly receives the door. This suggests more difficult sealing issues between the door and the container portion.
Wafers of larger dimensions will also have significantly greater sag which will make them more susceptible to damage during handling and transport and require unique support not required for smaller wafers. This greater sag presents challenges in maintaining the desired spacing between wafers while still allowing placement and removal of the wafers robotically by robotic arms and that are known as end effectors. Such devices are inserted between wafers in the front opening containers generally underneath a wafer to be grasped and removed. It is critical that there is no contact with the end effector with either adjacent wafer or the wafer container during insertion of the end effector to grasp the wafer. Once the wafer is grasped, removal must be accomplished without scraping or any contact by the end effector or wafer being removed with the adjacent wafers or container. Increased sagging of 450 mm wafers compared to 300 mm wafers make such retrieval and placement operations substantially more difficult in the 450 containers compared to 300 mm containers. Similarly, during placement of a wafer in a wafer container, no contact with adjacent wafers or the container is permissible. Current industry standards discussions and proposed standards by SEMI (Semiconductors Equipment and Materials International, a trade association) have tentatively allowed 68 degrees at the center rear of the wafer that is available for grasping (with at the very center rear for a wafer cushion feature) the 450 mm wafers. Such discussions and proposed standards also provide 72 degrees at the front center of the wafer for grasping or engagement by an end effector. Conventional front opening wafer containers provide front center, at least about 120 degrees of an access opening which may provide excessive front sag of the wafers making end effector insertion and engagement problematic.
Thus, it would be desirable to develop front opening configurations for 450 mm wafer containers that have design attributes for minimizing wafer sag and minimizing weight of the container. In addition, configurations providing improved sealing characteristics for the doors would be desirable. Moreover, configurations providing enhanced wafer support to accommodate storing of 450 mm wafers in wafer containers as well during robotic handling of the wafers would be desirable. Providing a container that minimizes the damage that could be caused to wafers by warpage or shrinkage of the shell components would also be desirable.